And we’re not even talking about the RNC. Seth Mnookin, in the New Yorker, on aging fathers and their degrading, mutant sperm:
Autism, as anyone who has ever written about the topic can attest, is a subject that provokes strong reactions. So it was no shock when a recent Nature study that clarified the well-established link between paternal age and a child’s risk for autism and schizophrenia got lots of attention. What was surprising was how that news, which one of the study’s lead authors described as “sort of a little bit of our side story,” obscured the implications of the paper’s main findings—namely, that the genetic health of the species is now facing a serious threat.
The study, by Kari Stefansson and his team at Decode Genetics, in Iceland, used an elegant application of brute-force genetic sequencing to show that approximately ninety-seven per cent of the difference in the rate of de-novo mutations can be attributed to the age of the father. These new mutations arise during the production of eggs or sperm. Since females are born with a lifetime supply of eggs already in their ovaries, the number of de-novo (or novel) mutations a mother passes down is roughly fifteen, regardless of how old she is. Male sperm-producing cells, on the other hand, are constantly dividing, and as a result, the number of spontaneous mutations increases over time.
For sociological and environmental reasons, men are living longer and having children when they’re older. That, combined with the fact that we’re living in an era of diminished pressure from natural selection, means that Stefansson and his colleagues may have identified the single biggest factor in the ongoing development of the human genome: new mutations caused by old sperm. Mutations can be beneficial, but they are much more likely to be harmful—which means the changes will be overwhelmingly negative.
“This is really scary,” Alexey Kondrashov, an evolutionary biologist at the University of Michigan, said last Thursday from Moscow. In a Nature commentary that accompanied the Decode study, Kondrashov raised the spectre of an inevitable “decline in the mean fitness of the population.” As it happens, it’s likely that this is already occurring. If you combine the findings of a 2009 PLOS ONE paper that examined the link between advanced paternal age and a decline in social and exploratory behaviors with Decode’s results, you get a scenario that is as alarming as it is plausible.
“Diagnoses of autism and schizophrenia is one thing, but [older fathers may have] a perfectly normal [child] in the sense that there may not be a diagnosis, but his IQ is 108 instead of 110,” Kondrashov says, noting that this hypothesis tracks with results from his own research on fruit flies. “This means this is a problem that will lead to very severe consequences for society over several generations.” Over the past several decades, these changes were likely masked by improvements in the environment—“getting rid of lead paint, fewer infections, less malnutrition, whatever”—but moving forward, Kondrashov says that he “strongly suspect our gene pool gets worse.”…